Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How we can prove boltzman constant?

  1. Jun 12, 2010 #1
    hello all

    if some one here can help me to prove boltzman costant

    from SI unit to reach that k= 1.0356 x 10-22 Torr-liter/K ?
  2. jcsd
  3. Jun 12, 2010 #2


    User Avatar
    Science Advisor

    I don't know how you can 'prove' an experimental value. But I can tell you how to measure it.

    Simplest way would just be to measure the Ideal Gas Constant, since that's just Boltzmann's constant in disguise ([tex]R = N_Ak_B[/tex]). Take a fixed amount of a relatively ideal gas (e.g. helium) at a fixed volume. Vary the temperature and measure the pressure. Plot p against T and the slope is N*kB.
  4. Jun 12, 2010 #3

    but i need just to calculate it ?
  5. Jun 12, 2010 #4


    User Avatar
    Science Advisor

    I don't know what you expect to calculate it from? It's a physical constant, not a mathematical one. It's the fundamental relationship between energy and temperature. For different units of either, it wouldn't be needed at all.

    The Kelvin scale of temperature is defined by the triple point of water, and so the Boltzmann constant in SI units is determined by that as well.
  6. Jun 12, 2010 #5
    we can start from this relation

    PV=N KT

    & use convert from SI unit to This unit but i dont reach for the same result
  7. Jun 12, 2010 #6


    User Avatar
    Science Advisor

    Oh sorry, I thought you meant to somehow calculate it. You're saying you want to convert units.

    Well if your pressure and volume is in SI units, pV = Pa*m3, so if you want it in Torr-liters you want to multiply by Pascal/Torr and liters/m3.
    So (1/133.322368)*1000.

    So 1.3806504E-23 (Pa*m3) =1.380‚ÄČ6504E-23*(1000/133.322368) (Torr*Liters) = 1.03513E-22 (Torr*Liters)
  8. Jun 13, 2010 #7
    yes , right

    but i dont understand
    1.3806504E-23 (Pa*m3)
    how you found it
    if u can explane to me more
  9. Jun 13, 2010 #8


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    That is the accepted value in SI units, which anybody can find using Google. The value is given by many sources:
    It is not clear what the source of your confusion is. Do you want to know:
    • How is k determined experimentally?
    • Where can you look up the value of k?
    • Why are the units Pa*m3/K ?
    • Other?
  10. Jun 15, 2010 #9

    we can find that from Boyle's Law

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook